Acoustic and electromagnetic shield and mechanical support for ultrasonic strip delay line

ABSTRACT

An ultrasonic strip delay line having its longitudinal edges covered with acoustic absorbing tape is coiled with a dummy shielding strip and placed between clamping plates. The dummy strip provides a mechanical stop which prevents distortion of the delay line as well as a grounded metal enclosure for electromagnetic and acoustic shielding of the delay line.

United States Patent [54] ACOUSTIC AND ELECTROMAGNETIC SHIELD AND MECHANICAL SUPPORT FOR ULTRASONIC STRIP DELAY LINE 6 Claims, 2 Drawing Figs. [52] US. Cl 333/30, 3 36/ l 99 [51] Int. Cl H03h 9/30 [50] Field of Search 333/29, 30, 30 (M); 336/199, 206, 207

[56] References Cited UNITED STATES PATENTS 3,320,555 5/1967 Allen 333/30X Primary Examiner-Herman Karl Saalbach Assistant ExaminerSaxfield Chatmon, .lr. Att0rney-Louis Etlinger ABSTRACT: An ultrasonic strip delay line having its longitudinal edges covered with acoustic absorbing tape is coiled with a dummy shielding strip and placed between clamping plates. The dummy strip provides a mechanical stop which prevents distortion of the delay line as well as a grounded metal enclosure for electromagnetic and acoustic shielding of the delay line.

PAIENTEMYIBM D 1 '3579'151 FIGZ INVENTORS DAVID J. WHITNEY RAYMOND R. NEPVEU AGENT ACOUSTIC AND ELECTROMAGNETIC SHIELD AND MECHANICAL SUPPORT FOR ULTRASONIC STRIP DELAY LINE BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates generally to the field of ultrasonic strip delay lines and in particular to an improved acoustic and electromagnetic shield and mechanical support for such delay lines.

2. Description of the Prior Art Prior to the present invention metal strip-type acoustic delay lines providing relatively long delays such as those used in pulse compression systems were generally packaged in a coiled arrangement wherein many turns were simply wrapped closely adjacent one another. Several problems attend this approach to delay line packaging; specifically, experience has shown that there is coupling of acoustic energy through the air gap between adjacent turns of the delay line which causes spurious signals at the output terminal both before and after the main output pulse. The time spacing of the spurious signals or sidelobes from the main output pulse is'the time required for the acoustic wave to travel around one turn of the coil. Another problem encountered with the prior art coiled strip delay lines is electromagnetic coupling between the input and output transducers which is commonly termed direct feedthrough. Yet another problem which has been experienced with prior art coiled delay lines is the spurious signals which are generated due to slight mechanical distortion of the coil when it is clamped in place for the purpose of isolating the line from shock and vibration.

OBJECTS AND SUMMARY OF THE INVENTION It is therefore a primary object of the present invention to provide a new and novel method and apparatus for packaging ultrasonic strip delay lines.

It is another object of the present invention to provide apparatus of the above described character wherein adjacent turns of a coiled delay line are acoustically isolated from one another.

It is an additional object of the present invention to provide apparatus of the above described character wherein electromagnetic coupling between input and output transducers is substantially eliminated.

It is a further object of the present invention to provide apparatus of the above described character which mechanically supports said delay line.

These and other objectives of the invention are achieved by providing a strip delay line coiled simultaneously with an inert or dummy shielding strip of slightly larger transverse dimension than the delay line. Acoustic absorbing tape is applied to the longitudinal edges of the delay line and the coiled assembly is clamped between parallel plates. The dummy shielding strip provides means for mounting an RF connector at each end and also provides electromagnetic shielding of the input and output transducers.

The foregoing as well as other objects, features and advantages of the present invention will become more apparent from the following detailed description taken in conjunction with the appended drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a longitudinal cross section view of an ultrasonic strip delay line and shielding strip packaged in accordance with the principles of the present invention.

FIG. 2 is a transverse cross section view of the apparatus of FIG. 1.

DESCRIPTION OF PREFERRED EMBODIMENT Turning now to FIG. 1 there is illustrated an ultrasonic strip delay line which is coiled simultaneously with an inert or dummy shielding strip 12. The strip 12 is of a slightly larger transverse dimension than the delay line 10 and is terminated at either end in housings 14 and 16 which provide a means for mounting RF input and output connectors 18 and 20 as well as an electromagnetic shield for the input and output transducers 22 and 24 which are disposed at each end of the delay line 10. The dummy strip 12 may be fabricated of the same material as the delay line 10 such as aluminum and in practice may be slightly thinner and is slightly wider than the delay line itself.

FIG. 2 is a transverse cross section view of the apparatus of FIG. 1 and more clearly illustrates the physical relationship between the elements of the invention. A layer 26 of acoustic absorbing material such as 028 tape which is commercially available from the Minnesota Mining and Manufacturing Company is applied to the longitudinal edges of the delay line 10 to form a U-shaped channel. The absorbing material serves the purposes of providing acoustic absorption at the edge of the delay line 10, providing a physical radial spacing between the dummy strip 12 and the delay line 10 and providing a physical cushion between the delay line 10 and the clamping plates 28 and 30 used to hold the coil in place. An additional layer 27 of absorbing material is applied to the dummy strip 12 for the purpose of providing additional radial spacing between the delay line 10 and dummy strip 12. The layer 27 of absorbing material is not, however, carried over the longitudinal edges of the dummy strip 12 so that it may make firm electrical and mechanical contact with the clamping plates 28 and 30. The dummy strip I2 thus provides a positive mechanical stop which prevents distortion of the delay line 10 during clamping, a well grounded metallic enclosure for electromagnetic shielding of the transducers 22 and 24 and an efficient acoustic shield between adjacent turns of the delay line 10.

As an illustrative example of the improvement provided by the present invention two delay lines were fabricated by the Applicants; one delay line merely had its longitudinal edges covered with acoustic absorbing material and another was fabricated in accordance with the principles of the present invention as set forth hereinabove. Both delay lines were formed of 5052H32 aluminum 1.75 inches wide, 24.5 mils maximum thickness and 20 feet long wrapped in a coil of about 8 inches in diameter. The best sidelobe rejection observed was about 40 db. in the frequency range from 2.3 to 5.0 MHz. When the delay line was coiled simultaneously with a dummy strip of 5052H32 aluminum, 20 mils wider than the delay line and 19 mils thick, sidelobe suppression of about 60 db. or an improvement of about 20 db. was readily achieved. N0 distortion of the delay line or of the delay line output signal due to the clamping plates was observable and direct feed-through was reduced to an unobservable level.

It will thus be seen that the Applicants have provided a new and novel method and apparatus'for mounting ultrasonic strip delay lines whereby acoustic and electromagnetic shielding and mechanical support is provided and whereby a significant improvement in spurious signal rejection is achieved. Since certain changes in the above described construction will become apparent to those skilled in the art it is intended that all matter contained in the foregoing description or shown in the appended drawings shall'be interpreted as illustrative and not in a limiting sense.

We claim:

I. Apparatus for mounting ultrasonic strip delay lines comprising:

an inert shielding strip of larger transverse dimension than said delay line coiled simultaneously with said delay line, and

a radial spacing means between said delay line and said inert strip formed of a layer of acoustic absorbing material disposed about the longitudinal edges of said delay line and extending along each surface thereof a preselected distance less than the transverse dimension of said delay line.

2. Apparatus as recited in claim I further including means integrally formed in each end of said inert strip for mounting input and output signal connectors and means for coupling said connectors to said delay line.

relationship with respect to one another.

6. Apparatus as rectified in claim 1 further including a layer of acoustic absorbing material disposed longitudinally along a portion of each surface of said inert strip proximate the longitudinal edge thereof and extending transversely across said strip a preselected distance less than the transverse dimension of said strip. 

1. Apparatus for mounting ultrasonic strip delay lines comprising: an inert shielding strip of larger transverse dimension than said delay line coiled simultaneously with said delay line, and a radial spacing means between said delay line and said inert strip formed of a layer of acoustic absorbing material disposed about the longitudinal edges of said delay line and extending along each surface thereof a preselected distance less than the transverse dimension of said delay line.
 2. Apparatus as recited in claim 1 further including means integrally formed in each end of said inert strip for mounting input and output signal connectors and means for coupling said connectors to said delay line.
 3. Apparatus as recited in claim 2 wherein said mounting means is disposed relative to said coupling means such that an electromagnetic shield is formed about said coupling means.
 4. Apparatus as recited in claim 1 wherein said delay line and said inert strip are formed of the same material.
 5. Apparatus as recited in claim 1 further including means in electrical and mechanical contact with said inert strip for clamping said delay line and said inert strip in a fixed spatial relationship with respect to one another.
 6. Apparatus as rectified in claim 1 further including a layer of acoustic absorbing material disposed longitudinally along a portion of each surface of said inert strip proximate the longitudinal edge thereof and extending transversely across said strip a preselected distance less than the transverse dimension of said strip. 